Usually, the device node /dev/null has a full set of Write permissions. This is required by some printer drivers, like UFR2, because CUPS works as a non-root user. If the UFR2 driver does not have permission to write to /dev/null, it will fail.

But when you remaster a Puppy, like Wolx, these permissions sometimes disappear. The "chmod 666" command restores the Write permissions to /dev/null.